MUC1 and breast cancer: Overexpression of MUC1, as found in breast cancer cells, is also associated with resistance to apoptosis in response to genotoxic anticancer agents.30 Other reports have demonstrated that MUC1 expression is increased in breast cancer cells that form mammospheres.31 We tested two small interfering RNAs (siRNAs) that targeted different places of MUC1 and confirmed effective blockage of MUC1-C level in the first siRNA (Supplementary Figure S1B).